1. Field of the Invention
The present invention relates to an apparatus such as an ink-jet printer capable of ejecting very small droplets.
2. Description of Related Art
In ink-jet printers, it is desired that each ink droplet to be ejected from a printing head is as small as possible in order to improve print quality. From this viewpoint, an existing ink-jet printing head can eject small ink droplets of about 2 pl by, for example, devising a control pulse waveform for an actuator to apply ejection energy to ink, or decreasing the diameter of each nozzle.
In recent years, however, it is required to eject very small ink droplets of less than 2 pl to realize higher-quality, higher-resolution print. By the above-described technique of devising a control pulse waveform or decreasing the diameter of each nozzle, however, it is difficult to further decrease the size of each ink droplet.
Other than the above-described techniques, there is known a technique to regulate a control pulse waveform and, at the same time, to regulate a distance between the nozzle and a print medium such that a main dot (a main ink droplet) and a satellite dot (a satellite ink droplet), both of which are ejected through a nozzle in accordance with one pressure variation, may have substantially the same weight and such that landing positions of those two ink droplets may be different from each other. (see Japanese Patent Application Laid-open No. 7-285222). By this technique, the size of the main ink droplet can be decreased, besides the satellite ink droplet can be increased in size and thus this can be a dot independent of the main dot.
However, for printing an image at a very high resolution having, e.g., photographic quality, it is required to eject ink droplets each smaller than those obtained by the above-described technique. In addition, other than the requirement of ejecting very small ink droplets, there may be a requirement for an ink-jet printer to eject very small droplets of conductive paste and thereby print a very fine electric circuit on a substrate.